U.S. patent application number 16/660542 was filed with the patent office on 2020-04-23 for optical engine for three-dimensional printing.
The applicant listed for this patent is Texas Instruments Incorporated. Invention is credited to Stephen Aldridge Shaw, Zhongyan Sheng, Steven Edward Smith.
Application Number | 20200122394 16/660542 |
Document ID | / |
Family ID | 70280386 |
Filed Date | 2020-04-23 |
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United States Patent
Application |
20200122394 |
Kind Code |
A1 |
Sheng; Zhongyan ; et
al. |
April 23, 2020 |
OPTICAL ENGINE FOR THREE-DIMENSIONAL PRINTING
Abstract
A spatial light modulator outputs modulated light including:
modulated first light when the spatial light modulator receives
first light; and modulated second light when the spatial light
modulator receives second light. Projection optics project the
modulated light onto: a first pixel region when a component or the
spatial light modulator has a first position; and a second pixel
region when the component or the spatial light modulator has a
second position. The first and second pixel regions partially
overlap. A pixel shifter moves the component or the spatial light
modulator between: the first position when the spatial light
modulator outputs the modulated first light; and the second
position when the spatial light modulator outputs the modulated
second light.
Inventors: |
Sheng; Zhongyan; (Allen,
TX) ; Shaw; Stephen Aldridge; (Plano, TX) ;
Smith; Steven Edward; (Allen, TX) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Texas Instruments Incorporated |
Dallas |
TX |
US |
|
|
Family ID: |
70280386 |
Appl. No.: |
16/660542 |
Filed: |
October 22, 2019 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
62749215 |
Oct 23, 2018 |
|
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G02B 3/0037 20130101;
B29C 64/129 20170801; B33Y 10/00 20141201; B29C 64/277 20170801;
G02B 26/0833 20130101; B33Y 30/00 20141201 |
International
Class: |
B29C 64/277 20060101
B29C064/277; B33Y 10/00 20060101 B33Y010/00; B33Y 30/00 20060101
B33Y030/00; B29C 64/129 20060101 B29C064/129 |
Claims
1. A device, comprising: a light source configured to provide a
first light and a second light; a spatial light modulator optically
coupled to the light source, the spatial light modulator configured
to modulate the first light and the second light and to output
modulated light including: a modulated first light when the light
source provides the first light; and a modulated second light when
the light source provides the second light; projection optics
having a component, the projection optics optically coupled to the
spatial light modulator and adapted to be optically coupled to a
target having first and second pixel regions that partially
overlap, the projection optics configured to project the modulated
light onto the first pixel region when the component or the spatial
light modulator has a first position, and to project the modulated
light onto the second pixel region when the component or the
spatial light modulator has a second position; and a pixel shifter
coupled to the component or the spatial light modulator, the pixel
shifter configured to move the component or the spatial light
modulator between: the first position when the spatial light
modulator outputs the modulated first light; and the second
position when the spatial light modulator outputs the modulated
second light.
2. The device of claim 1, wherein the first light has a first
intensity, and the second light has a second intensity equal to the
first intensity.
3. The device of claim 1, wherein the light source is a light
emitting diode.
4. The device of claim 1, wherein the spatial light modulator is a
digital micromirror device.
5. The device of claim 1, wherein the target is a resin, the first
light has a first intensity below a curing threshold of the resin,
the second light has a second intensity below the curing threshold,
and a sum of the first and second intensities exceeds the curing
threshold.
6. The device of claim 5, wherein the resin is a photo-polymerizing
resin.
7. The device of claim 1, wherein the pixel shifter is coupled to
the spatial light modulator and is configured to move the spatial
light modulator between the first and second positions, so the
spatial light modulator has the first position when the spatial
light modulator outputs the modulated first light, and the spatial
light modulator has the second position when the spatial light
modulator outputs the modulated second light.
8. The device of claim 1, wherein the pixel shifter is coupled to
the component and is configured to move the component between the
first and second positions, so the component has the first position
when the spatial light modulator outputs the modulated first light,
and the component has the second position when the spatial light
modulator outputs the modulated second light.
9. The device of claim 1, wherein the pixel shifter is a refractive
device.
10. The device of claim 1, wherein the pixel shifter is a
reflective device.
11. A three-dimensional printer comprising: a resin vat having a
transparent bottom; a lift plate insertable within the resin vat; a
light source configured to provide a first light and a second
light; a spatial light modulator optically coupled to the light
source, the spatial light modulator configured to modulate the
first light and the second light and to output modulated light
including: a modulated first light when the light source provides
the first light; and a modulated second light when the light source
provides the second light; projection optics having a component,
the projection optics optically coupled to the spatial light
modulator and adapted to be optically coupled through the
transparent bottom to a resin on the lift plate, the resin having
first and second pixel regions that partially overlap, the
projection optics configured to project the modulated light onto
the first pixel region when the component or the spatial light
modulator has a first position, and to project the modulated light
onto the second pixel region when the component or the spatial
light modulator has a second position; and a pixel shifter coupled
to the component or the spatial light modulator, the pixel shifter
configured to move the component or the spatial light modulator
between: the first position when the spatial light modulator
outputs the modulated first light; and the second position when the
spatial light modulator outputs the modulated second light.
12. The three-dimensional printer of claim 11, wherein the first
light has a first intensity, and the second light has a second
intensity equal to the first intensity.
13. The three-dimensional printer of claim 11, wherein the spatial
light modulator is a digital micromirror device.
14. The three-dimensional printer of claim 11, wherein the pixel
shifter is coupled to the spatial light modulator and is configured
to move the spatial light modulator between the first and second
positions, so the spatial light modulator has the first position
when the spatial light modulator outputs the modulated first light,
and the spatial light modulator has the second position when the
spatial light modulator outputs the modulated second light.
15. The three-dimensional printer of claim 11, wherein the pixel
shifter is coupled to the component and is configured to move the
component between the first and second positions, so the component
has the first position when the spatial light modulator outputs the
modulated first light, and the component has the second position
when the spatial light modulator outputs the modulated second
light.
16. The three-dimensional printer of claim 11, wherein the pixel
shifter is a refractive device.
17. The three-dimensional printer of claim 11, wherein the pixel
shifter is a reflective device.
18. The three-dimensional printer of claim 11, wherein the first
light has a first intensity below a curing threshold of the resin,
the second light has a second intensity below the curing threshold,
and a sum of the first and second intensities exceeds the curing
threshold.
19. The three-dimensional printer of claim 18, wherein the resin is
a photo-polymerizing resin.
20. A method comprising: with a spatial light modulator, outputting
modulated light including: modulated first light when the spatial
light modulator receives first light; and modulated second light
when the spatial light modulator receives second light; with
projection optics having a component, projecting the modulated
light onto: a first pixel region when the component or the spatial
light modulator has a first position; and a second pixel region
when the component or the spatial light modulator has a second
position, in which the first and second pixel regions partially
overlap; and moving the component or the spatial light modulator
between: the first position when the spatial light modulator
outputs the modulated first light; and the second position when the
spatial light modulator outputs the modulated second light.
21. The method of claim 20, wherein the spatial light modulator is
a digital micromirror device.
22. The method of claim 20, wherein moving the component or the
spatial light modulator includes moving the spatial light modulator
between the first and second positions, so the spatial light
modulator has the first position when the spatial light modulator
outputs the modulated first light, and the spatial light modulator
has the second position when the spatial light modulator outputs
the modulated second light.
23. The method of claim 20, wherein moving the component or the
spatial light modulator includes moving the component between the
first and second positions, so the component has the first position
when the spatial light modulator outputs the modulated first light,
and the component has the second position when the spatial light
modulator outputs the modulated second light.
24. The method of claim 20, wherein the first and second pixel
regions are located on a resin, the first light has a first
intensity below a curing threshold of the resin, the second light
has a second intensity below the curing threshold, and a sum of the
first and second intensities exceeds the curing threshold.
25. The method of claim 24, wherein the resin is a
photo-polymerizing resin.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims the benefit under 35 U.S.C. .sctn.
119(e) to co-owned U.S. Provisional Patent Application Ser. No.
62/749,251, filed Oct. 23, 2018, entitled "ENHANCED 3D PRINTING
USING PIXEL LEVEL SCAN," which is hereby incorporated herein by
reference in its entirety.
TECHNICAL FIELD
[0002] This relates generally to three-dimensional printing, and in
examples, to stereolithographic apparatus (SLAs).
BACKGROUND
[0003] Three-dimensional printing is useful in many fields, such as
manufacturing and artistic design. The cost of three-dimensional
printing is falling; thus, making more and more applications for
this technology financially feasible. One type of three-dimensional
printer is the photo-polymerization printer or stereolithographic
apparatus (SLA). This type of printer uses light to convert a
liquid polymer to a solid. One type of photo-polymerization printer
is a vat type. This type of printer uses a vat with a transparent
bottom to contain photo-polymerizable liquid. Initially, a lift
plate is one layer from the bottom of the vat. Each printer has a
layer thickness that the printer develops, which may be tens to
hundreds of microns thick. An optical engine is below the vat. The
optical engine uses light to expose a pattern for the initial layer
derived from a three-dimensional electronic model of the object to
be printed. The light causes the liquid in the vat to polymerize in
that pattern and thus form solid material. The lift plate then
rises a layer and then exposes the next layer of the object. This
process repeats until the printer forms all layers of the
object.
[0004] With photo-polymerization printers, the optical engine can
produce layers with high resolution. For example, a digital light
processing (DLP) optical engine can produces patterns with millions
of pixels. However, the optical resolution of the spatial light
modulator limits resolution of the printed device.
SUMMARY
[0005] A spatial light modulator outputs modulated light including:
modulated first light when the spatial light modulator receives
first light; and modulated second light when the spatial light
modulator receives second light. Projection optics project the
modulated light onto: a first pixel region when a component or the
spatial light modulator has a first position; and a second pixel
region when the component or the spatial light modulator has a
second position. The first and second pixel regions partially
overlap. A pixel shifter moves the component or the spatial light
modulator between: the first position when the spatial light
modulator outputs the modulated first light; and the second
position when the spatial light modulator outputs the modulated
second light.
BRIEF DESCRIPTION OF THE DRAWINGS
[0006] FIG. 1 is a diagram of a three-dimensional printer.
[0007] FIG. 2 is a diagram of an example optical engine.
[0008] FIGS. 3A-3C (collectively "FIG. 3") are diagrams showing
example shifting pixels.
[0009] FIG. 4 is a diagram showing two example curing
strategies.
[0010] FIG. 5 is a diagram of an example process to extend the
cured area of the process of FIG. 4.
[0011] FIG. 6 is a diagram showing an example result of forming a
more complex feature with a fixed pixel size.
[0012] FIG. 7 is a diagram of the result of forming a pattern using
an example process.
[0013] FIG. 8 is a diagram showing an example of the process of
FIG. 7 with smaller subpixels.
[0014] FIGS. 9A-9D (collectively "FIG. 9") are diagrams of an
example process using an analog pixel shift.
[0015] FIGS. 10A-10E (collectively "FIG. 10") are diagrams of
another example process using an analog pixel shift.
[0016] FIG. 11 is a diagram of an example arrangement of an optical
engine within a three-dimensional printer.
[0017] FIG. 12 is a diagram of an example optical engine.
[0018] FIG. 13 is a diagram of another example optical engine.
[0019] FIG. 14 is a diagram of another example optical engine.
[0020] FIGS. 15A-15B (collectively "FIG. 15") are diagrams of a
mirror/actuator combination.
[0021] FIGS. 16A-16B (collectively "FIG. 16") are diagrams of
another mirror/actuator combination.
[0022] FIGS. 17A-17C (collectively "FIG. 17") are diagrams of an
example pixel shifter using two flat plates.
[0023] FIG. 18A-18C (collectively "FIG. 18") are views of an
example beam direction device for pixel shifting.
[0024] FIG. 19 is a process flow diagram of an example process.
DETAILED DESCRIPTION
[0025] In the drawings, corresponding numerals and symbols
generally refer to corresponding parts unless otherwise indicated.
The drawings are not necessarily drawn to scale.
[0026] In this description, the term "coupled" may include
connections made with intervening elements, and additional elements
and various connections may exist between any elements that are
"coupled." Elements are referred to herein as "optically coupled"
when a connection between the elements involves transmission or
reception of light.
[0027] In example arrangements, the problem of providing finer
resolution in three-dimensional printing is solved by using
illumination below a curing threshold and overlapping at least two
pixels so that the combined illumination in the overlapped area is
above the curing threshold. In an example, a spatial light
modulator outputs modulated light including: modulated first light
when the spatial light modulator receives first light; and
modulated second light when the spatial light modulator receives
second light. Projection optics project the modulated light onto: a
first pixel region when a component or the spatial light modulator
has a first position; and a second pixel region when the component
or the spatial light modulator has a second position. The first and
second pixel regions partially overlap. A pixel shifter moves the
component or the spatial light modulator between: the first
position when the spatial light modulator outputs the modulated
first light; and the second position when the spatial light
modulator outputs the modulated second light.
[0028] FIG. 1 is a diagram of a three-dimensional printer 100.
Three-dimensional printer 100 prints a three-dimensional object
layer-by-layer from an electronic model of the object. Vat 102 has
a transparent bottom. Control arm 106 positions lift plate 104 in
vat 102. Photo-polymerizing resin 108 fills vat 102. Control arm
106 positions lift plate 104 at a layer thickness 110 from the
bottom of vat 102. In examples, the layer thickness is 0.05 to 0.15
mm. When the lift plate is in position, optical engine 112 projects
light in a pattern of the first layer of the object to be printed.
Where light from the optical engine 112 strikes photo-polymerizing
resin 108, photo-polymerizing resin polymerizes and forms solid
material. Thus, the first layer of the object to be printed is
formed.
[0029] The first layer adheres to lift plate 104. Control arm 106
then lifts lift plate 104 by another layer thickness 110. In some
examples, control arm 106 lifts, twists and/or tilts lift plate 104
to release the first layer from the bottom of vat 102. When the
lift plate 104 is in position for the next layer of the object,
optical engine 112 projects light in the pattern of the next layer
of the object. Three-dimensional printer 100 repeats this process
until all layers of the object are printed.
[0030] FIG. 2 is a diagram of an example optical engine 212.
Optical engine 212 is like optical engine 112 (FIG. 1). Light
source 202 is a light emitting diode (LED) in this example. In
other examples, light source 202 is another source of light, such
as laser diode or a high intensity incandescent light. In this
example, the LED produces 1255 mW of optical power. The wavelength
of light produced by light source 202 is selected for efficient
polymerization of photo-polymerizing resin 108 (FIG. 1). In this
example, light source 202 produces light of approximately 405 nm.
In other examples, light source 202 produces light in a range of
350-460 nm. In many light sources for optical engines, light from
the light source is collimated at the output of the light source.
However, this requires additional lenses at the output of light
source 202. In this example, the input of light integrator 204 is
proximate to light source 202. This captures as much light as
possible without the need for collimating lenses. In addition, in
this example, the form factor of the input of light integrator 204
is approximately the same as the form factor of the output of light
source 202, which increases the portion of light from light source
202 that enters light integrator 204.
[0031] The output of light integrator 204 is larger than the input
of light integrator 204. This configuration lowers the spread of
light from the output of light integrator 204 so that the light is
efficiently provided to spatial light modulator 210. Light
integrator 204 homogenizes the light from light source 202 by
multiple reflections of the light inside light integrator 204. In
addition, light integrator 204 helps direct as much light as
possible onto spatial light modulator 210. As used herein, the term
"light integrator" includes light tunnels, integrating rods, light
pipes, and compound parabolic concentrators. Although other types
of devices perform light integration, such as micro-lens arrays,
these other types of devices are not included in the term "light
integrator" as used herein. In this example, light integrator 204
is a light tunnel.
[0032] Divergent light from the output of light integrator 204
passes through cover prism 206. The divergent light from the output
of light integrator 204 has a form that roughly matches the form
factor of spatial light modulator 210. Cover prism 206 provides a
surface that is perpendicular to the propagation path of the output
of light integrator 204 to lower distortion of the form of light
output from light integrator 204. In addition, the higher
refractive index of cover prism 206 relative to air lowers the
divergence of the light from the output of light integrator 204.
The light then passes through an air gap 207 and through reverse
total internal reflection prism (RTIR prism) 208. In this example,
spatial light modulator 210 is a digital micromirror device (DMD).
Other examples use other spatial light modulators, such as liquid
crystal on silicon (LCOS) modulators. With DMDs, each pixel is a
movable mirror that modulates light by reflecting in an ON
direction or an OFF direction, depending on the data for that pixel
provided to the DMD. Thus, spatial light modulator 210 addresses
multiple pixel positions. The angle of the surface of RTIR prism
208 closest to light integrator 204 is such that it reflects ON
direction light from pixels reflecting of spatial light modulator
210 but does not reflect light from light integrator 204.
Therefore, the image for projection reflects from RTIR prism 208 to
projection optics 214. Projection optics 214 includes components
such as at least one lens and/or a pupil. As noted above, the light
from light source 202 is not collimated before light integrator
204. The pixels of spatial light modulator 210 are mirrors,
therefore modulated divergent output light 216 is also divergent as
it enters projection optics 214. Projection optics are often
telecentric and thus designed for non-divergent and non-convergent
(i.e. collimated) light that has an infinite input focal distance.
In this example, modulated divergent output light 216 is divergent,
so projection optics 214 must have an input focal point directed to
the point of divergence, and thus is non-telecentric. Because light
integrator 204 modifies the divergence of the light from light
source 202, the point of divergence or input focal point is
calculated using the angle of divergence of the light at the output
of light integrator 204. The output of projection optics 214
focuses on a target 218. That is, the focal point of projection
optics 214 is on the photo-polymerizing resin 108 (FIG. 1) between
the lift plate 104 (FIG. 1) and the bottom of vat 102 (FIG. 1). In
an example, projection optics 214 may include five lenses using
N-BK7 glass. In this example, the five lenses are spherical. In an
example, projection optics 204 has an f-number of 3. Co-pending
non-provisional patent application (TI-79946) includes further
details of the example of FIG. 2.
[0033] FIGS. 3A-3C (collectively "FIG. 3") are diagrams showing
example shifting pixels. As shown in FIG. 3A, pixel 302 is an image
or light signal provided by the reflection from one pixel of a
spatial light modulator like spatial light modulator 210 (FIG. 2).
As shown in FIG. 3B, pixel 304 is another pixel image along with
pixel 306. Pixel 306 is a light signal provided by the same pixel
of spatial light modulator 210 (FIG. 2) but shifted in both the x
and y directions. This leaves an overlap 308 illuminated by both
pixel 304 and pixel 306. As is further explained hereinbelow, if
total illumination intensity (illumination level multiplied by the
illumination time) for pixel 304 and pixel 306 is less that a
curing threshold of photo-polymerizing resin 108 (FIG. 1) but the
combined total illumination intensity of pixel 304 and 306 is
greater than the curing threshold, only overlap 308 is cured, thus
curing an area that is smaller (higher resolution) than pixel 304
or pixel 306. In FIG. 3B, pixel 304 and pixel 306 have overlap on
9/16 of the size of pixel 304 and pixel 306. However, this example
may use other size overlaps. In addition, the pixel may shift more
than once. For example, as shown in FIG. 3C, pixel 310 may provide
one fifth of the curing threshold total illumination intensity.
This pixel shifts to pixel 312 in both the x and y directions,
which also provides one fifth of the curing threshold total
illumination intensity. The pixel then shifts in the x direction to
pixel 314, which also provides one fifth of the curing threshold
total illumination intensity. This pixel then shifts in the y
direction to pixel 316, which also provides one fifth of the curing
threshold total illumination intensity. This pixel then shifts in
the x direction to pixel 318, which also provides one fifth of the
curing threshold total illumination intensity. The only portion
covered by each of pixel 310, pixel 312, pixel 314, pixel 316 and
pixel 318 is area 320. Therefore, area 320 is the only area that
receives a full threshold curing illumination intensity. Thus, this
example only cures area 320, which is a much smaller area (higher
resolution) than the pixel (pixel 310, pixel 312, pixel 314, pixel
316 and pixel 318) used to illuminate area 320.
[0034] FIG. 4 is a diagram showing two example curing strategies.
Strategy 400 creates a curing pattern one pixel wide and eight
pixels long. Illumination intensity 402 is an intensity above
curing threshold 404 across the width of pixels 406. Thus, strategy
400 produces a line of eight pixels long and one pixel wide in the
photo-polymerizing resin 108 (FIG. 1). This produces a line
one-pixel wide P. On the other hand, strategy 410 applies an
illumination intensity 412 that is below curing threshold 404 in a
first pixel position 414, and then shifts to a second pixel
position 416 and applies the illumination intensity 412 again.
Thus, in this example, the first pixel position and the second
pixel position receive the same illumination intensity. The area of
overlap Q between first pixel position 414 and second pixel
position 416 receives twice the illumination intensity 412, which
is above the curing threshold 404. Because overlap Q is the only
region that receives an illumination intensity above the curing
threshold 404, a line eight pixels long and overlap Q wide forms in
the photo-polymerizing resin 108 (FIG. 1). Thus, strategy 410
produces a line that has a higher resolution than strategy 400.
[0035] FIG. 5 is a diagram of an example process to extend the
cured area of the process of FIG. 4. Step 510 is like strategy 410
(FIG. 4). Threshold 504 is like curing threshold 404 (FIG. 4). In
step 520, either the original eight pixels shift to the right or
adjacent pixels are already in or are shifted to the position of
pixels 522. The example then applies illumination level 512 to
pixels 522. Illumination profile 524 is like the illumination
profile of strategy 410 of FIG. 4. Adding the illumination
intensity of pixels 522 creates illumination profile 526, which
adds a width Q to the portion of the photo-polymerizing resin 108
(FIG. 1) cured in step 510. Therefore, this example cures a 2 Q
wide line, where Q is a width less than the resolution of pixels
522. In step 530 either the original eight pixels shift to the
right or adjacent pixels are already in or are shifted to the
position of pixels 532. Pixels 532 provide an illumination
intensity of 512. This illumination intensity along with the
illumination profile 526 produces illumination profile 536, with a
cured region of photo-polymerizing resin 108 (FIG. 1) having a
width of 3 Q. Thus, the process steps of FIG. 5 can form a feature
of any desired width.
[0036] FIG. 6 is a diagram showing an example result of forming a
more complex feature with a fixed pixel size. Pixels 602 are
squares that a 0.1 mm on a side. The pattern being cured is quarter
circular pattern 604. A shown in FIG. 6, the curvature of pattern
604 does not match well with pixel 606, pixel 608 and pixel 610.
Thus, using pixels 602 to produce pattern 604 creates a sawtooth
pattern formed by pixels 606, 608 and 610.
[0037] FIG. 7 is a diagram of the result of forming a pattern 704
using an example process. In this example, pixel shifting and below
curing threshold illumination allows for curing of a portion of the
pixels like pixel 702. As shown in FIG. 7, each pixel, like pixel
702, includes sixteen addressable sub-pixels, like subpixel 712.
That is, the process shown in FIGS. 3-5 allows for addressing
subpixels like subpixel 712 with an above-threshold illumination
intensity. Using only those subpixels of pixel 706, pixel 708 and
pixel 710 that include pattern 704, produces a much smother and
accurate pattern.
[0038] FIG. 8 is a diagram showing an example of the process of
FIG. 7 with smaller subpixels. In the example of FIG. 8, pixel 802
includes sixty-four subpixels as opposed to the sixteen subpixels
of pixel 702 (FIG. 7). Thus, the process of FIG. 8 produces an even
more accurate depiction of pattern 804. The trade-off is that
dividing pixel 802 into sixty-four subpixels requires additional
shifting and exposure. Thus, using sixty-four subpixels is slower
than sixteen subpixels.
[0039] FIGS. 9A-9D (collectively "FIG. 9") are diagrams of an
example process using an analog pixel shift. As shown in FIG. 9A,
pattern 902 is a triangular pattern for reproduction in the cured
resin (like photo-polymerizing resin 108 (FIG. 1)). As shown in
FIG. 9B, array 904 shows the layout of pattern 902 onto an array of
pixels. Pixels 906 are uncured pixels and pixels 908 are cured
pixels. As shown, the edge of pattern 902 is a stair step using
this arrangement. As shown in FIG. 9C, array 910 shows an array of
pixels in an initial step of an example process. An illumination
intensity like illumination level 402 (FIG. 4) cures pixels 912. At
this step, pixels 914 are uncured. An illumination level applied to
pixels 916 is below the curing threshold. The pixels 916 shift left
("left" being relative to the page) by an amount such that the
upper left corners of the top pixels ("top" being relative to the
page) align with line 918 as shown by arrow 920. An analog shifting
mechanism (further explained hereinbelow) can shift the pixels by
any selected distance within the precision level of the shifting
mechanism and the driving circuitry. The analog shifting mechanism
then moves pixels 916 parallel to line 918 as shown by arrows 922.
One example illuminates pixels 916 while shifting. As shown in FIG.
9D, this produces a smooth line 930 between the uncured pixels 932
and the cured pixels 934. Another example shifts pixels 916 by a
selected amount before illumination. In this example, the smaller
the shift, the smoother line 930 will be. However, reducing the
shift increment increases the time necessary to cure the resin to
the desired configuration.
[0040] FIGS. 10A-10E (collectively "FIG. 10") are diagrams of
another example process using an analog pixel shift. As shown in
FIG. 10A, pattern 1002 is a quarter circle pattern for reproduction
in the cured resin (like photo-polymerizing resin 108 (FIG. 1)). In
other arrangements, the pixel density of the light modulation
limits the accuracy of pattern 1002. As shown in FIG. 10B, array
1004 shows the layout of pattern 1002 onto an array of pixels.
Pixels 1006 are uncured pixels and pixels 1008 are cured pixels. As
shown, the edge of pattern 1002 includes areas of varying size,
including large areas such as area 1012 and area 1014, that are
between cured pixels 1008 and the curvature 1010 of pattern 1002.
Ideally, a process cures the entire area within curvature 1010. As
shown in FIG. 10C, array 1020 shows the layout pattern 1002 shifted
to a best fit. That is, this shift mitigates the uncured area
inside the curvature 1010. Pixels 1026 are uncured pixels and
pixels 1028 are cured pixels. However, there remains significant
uncured area inside of curvature 1010 in array 1020.
[0041] As shown in FIG. 10D, array 1030 is an array like array
1020. Pixels 1036 are uncured pixels and pixels 1038 are cured
pixels. As noted above regarding array 1020, curing the whole
pixels within curvature 1010 leaves a significant area of uncured
pixels between cured pixels 1038 and the curvature 1010 of pattern
1002. To address these uncured pixels, this example selects the
cured pixels nearest curvature 1010 for pixel shifting. In the
example of array 1030, pixel 1040, pixel 1042, pixel 1044, pixel
1046, pixel 1048 and pixel 1050 shift. A pixel shifter shifts each
of the selected pixels, singularly or in various combinations, so
that the corner of these pixels touch curvature 1010. An analog
pixel shift (further explained hereinbelow) of the pixel position
of the spatial light modulator, as indicated by bi-directional
arrows 1052. This example applies an illumination strategy during
or between shifts of the selected pixels such that the total
illumination intensity of the uncured area between curvature 1010
and cured pixels 1038 is greater than the curing threshold 404
(FIG. 4). As shown in FIG. 10E, array 1041 shows that the result is
curing of the entire area 1054 under curvature 1010, while the area
1056 outside of curvature 1010 is uncured. Thus, the curing matches
the desired shape. The application of this example process is not
limited to any geometric shape or group of shapes.
[0042] FIG. 11 is a diagram on an example arrangement 1100 of an
optical engine within a three-dimensional printer. Optical engine
1112 is like optical engine 112 (FIG. 1). In the example of FIG.
11, mirror 1120 and mirror 1122 direct the light output by optical
engine 1112 to a target 1102 in a vat like vat 102 (FIG. 1).
[0043] FIG. 12 is a diagram of an example optical engine 1212.
Optical engine 1212 is like optical engine 212 of FIG. 2. Light
source 1202 illuminates spatial light modulator 1210 through light
tunnel 1204, prism 1206, and prism 1208. The modulated light
reflects from prism 1208, through projection optics 1214 to a
target. In examples, mirrors like mirror 1120 and mirror 1122 (FIG.
11) direct the output of projection optics 1214. In examples, an
actuator or actuators move elements of optical engine 1212 to
provide a pixel shift as described hereinabove. For example, an
actuator or actuators (described further hereinbelow) coupled to
prism 1206, prism 1208, spatial light modulator 1210, projection
optics 1214, pupil 1226, mirror 1120 (FIG. 11), and/or mirror 1122
moves one or more of these elements shifting the output pixel
position. The configuration of the actuator determines the
direction and amount of pixel shift.
[0044] FIG. 13 is a diagram of another example optical engine 1300.
Spatial light modulator 1302 provides a modulated image to lenses
1304. Mirror 1306 is a reflective device that reflects the image
from lenses 1304 to lenses 1308, which project the image to the
target. In this example, mirror 1306 serves as a pixel shifting
device. Mirror 1306 includes actuators (described further
hereinbelow) that tilt mirror 1306 in the x and/or y direction to
provide the desired pixel shift. FIG. 13 shows mirror 1306 in one
position, but other examples include mirror 1306 in different
places in the optical path of optical engine 1300. The selected
position may be based on size of the optical engine, effect on
optical quality or other design considerations.
[0045] FIG. 14 is a diagram of another example optical engine 1400.
Spatial light modulator 1402 provides a modulated image to lenses
1404. The image from lenses 1404 passes through a refractive device
like plate 1406 to lenses 1408 for projection. Plate 1406 includes
actuators (described further hereinbelow) that tilt plate 1406 in
the x and/or y direction to provide the desired pixel shift. FIG.
14 shows plate 1406 in one position, but other examples include
plate 1406 in different places in the optical path of optical
engine 1400. The selected position may be based on size of the
optical engine, effect on optical quality or other design
considerations.
[0046] FIGS. 15A and 15B (collectively "FIG. 15") are diagrams of a
mirror/actuator combination 1500. FIG. 15A is a side view and FIG.
15B is a top view through the mirror surface. The terms "side" and
"top" are used herein to describe the relationship between the
views and do not signify any other physical relationship. Piezo
electric element 1506, spring 1508, and pivots 1510 position mirror
1502 above base 1504. Selecting a voltage applied to piezo electric
element 1506 selects the tilt of mirror 1502 relative to base 1504.
Changing the tilt of a mirror, like mirror 1120 (FIG. 11), mirror
1122 (FIG. 11) or mirror 1306 (FIG. 13), changes the pixel
position. Using more than one mirror/actuator combination 1500 or
adding another piezo electric/pivot combination to mirror/actuator
combination 1500 allows for selecting a pixel shift in any
direction. The use of a piezo electric elements allows for a
precise pixel shift, either by increments or in an analog manner
because of the linear relationship of piezo electric size change to
applied voltage. A similar mechanism can be used with a plate, such
as plate 1406 (FIG. 14) but on an edge of the plate to avoid
impeding light through the plate. In addition, a similar mechanism
can apply a shift by moving any of the components of FIG. 12.
[0047] FIGS. 16A and 16B (collectively "FIG. 16") are diagrams of
another mirror/actuator combination 1600. FIG. 16A is a side view
and FIG. 16B is a top view through the mirror surface. The terms
"side" and "top" are used herein to describe the relationship
between the views and do not signify any other physical
relationship. Piezo electric element 1606 and spring 1608 position
mirror 1602 above base 1604. Selecting a voltage applied to piezo
electric element 1606 selects the tilt of mirror 1602 relative to
base 1604. Changing the tilt of a mirror, like mirror 1120 (FIG.
11), mirror 1122 (FIG. 11) or mirror 1306 (FIG. 13), changes the
pixel position. Using more than one mirror/actuator combination
1600 or adding another piezo electric/spring combination to
mirror/actuator combination 1600 allows for selecting a pixel shift
in any direction. The use of a piezo electric elements allows for a
precise pixel shift, either by increments or in an analog manner
because of the linear relationship of piezo electric size change to
applied voltage. A similar mechanism can be used with a plate, such
as plate 1406 (FIG. 14) but on an edge of the plate to avoid
impeding light through the plate. In addition, a similar mechanism
can apply a shift by moving any of the components of FIG. 12.
[0048] FIGS. 17A-17C (collectively "FIG. 17") are diagrams of an
example pixel shifter 1700 using two flat plates. As shown in FIG.
17A, plate 1702 tilts on an axis that is parallel to the x-axis
(i.e., into the page) as actuated by an actuator such as a piezo
electric actuator. Plate 1702 has an index of refraction n that is
greater than one (greater than air). The light travels on the
z-axis through plate 1702. Because the light is at an angle to the
surface of plate 1702 and because plate 1702 has an index of
refraction different from air, the light 1706 diffracts at an angle
.theta. at the interface between the air and the plate. Light 1706
then diffracts oppositely when exiting plate 1702. The result is a
shift of light 1706 by .DELTA.y, which is determined by
.DELTA.y=t=tn.sub.1/n.sub.2 sin .theta. (1)
where t is the thickness of plate 1702, n.sub.1 is the index of
refraction of air (which is 1), and n.sub.2 is the index of
refraction of plate 1702. Similarly, plate 1704 tilts on an axis
parallel to the y-axis as shown in FIG. 17B as actuated by an
actuator such as a piezo electric actuator. This creates a pixel
shift in the x-direction .DELTA.x in the same manner that plate
1702 creates a pixel shift in the y-direction. The combination of
shifts by plate 1702 and 1704 enables pixel shifting in any
direction in the x-y plane. FIG. 17C shows plate 1702 and plate
1704 in a perspective view.
[0049] FIGS. 18A-18C (collectively "FIG. 18") are views of an
example beam direction device for pixel shifting. As shown in FIG.
18A, Risley prism 1800 includes two wedge prisms: prism 1802 and
prism 1804. Rotating prism 1804 relative to prism 1802 changes the
direction of the light through Risley prism 1800. In FIG. 18A, the
wedged faces of prism 1802 and prism 1804 slope away from each
other from top to bottom. This configuration provides a maximum
deflection downward that Risley prism 1800 can provide. In FIG.
18B, prism 1804 turns ninety degrees from prism 1804 in FIG. 18A
with the thicker portion of prism 1804 away from the page. This
configuration provides less deflection. In FIG. 18C, the wedged
faces of prism 1802 and prism 1804 are parallel. This configuration
provides the minimal deflection. Thus, the deflection properties of
a Risley prism like Risley prism 1800 can accomplish pixel
shifting.
[0050] FIG. 19 is a process flow diagram of an example process
1900. Step 1902 is illuminating a first pixel position on a target
with a first illumination having a first illumination level less
than a threshold. The first pixel position is like pixel 304 (FIG.
3). The target is like target 218 (FIG. 2) or photo-polymerizing
resin 108 (FIG. 1). The first illumination level is like
illumination level 412 (FIG. 4). The threshold is like curing
threshold 404 (FIG. 4). Step 1904 is illuminating a second pixel
position on the target with a second illumination having a second
illumination level less than the threshold, wherein the first pixel
position and the second pixel position overlap and the sum of the
first illumination level and the second illumination level is
greater than the threshold. The second pixel position is like pixel
306 (FIG. 3). The second illumination level is light illumination
level 412 (FIG. 4). The overlap is like overlap 308 (FIG. 3).
[0051] Modifications are possible in the described examples, and
other examples are possible, within the scope of the claims.
* * * * *